Plasma processing method and plasma processing apparatus

ABSTRACT

At a time point T 0  when starting a process, a duty ratio of a high frequency power RF1 to which power modulation is performed is set to be an initial value (about 90%) which allows plasma to be ignited securely under any power modulating conditions. At the substantially same time of starting the process, the duty ratio of the high frequency power RF1 is gradually reduced from the initial value (about 90%) in a regular negative gradient or in a ramp waveform. At a time point t 2  after a lapse of a preset time T d , the duty ratio has an originally set value D s  for an etching process. After the time point t 2 , the duty ratio is fixed or maintained at the set value D s  until the end (time point T 4 ) of the process.

TECHNICAL FIELD

The embodiments described herein pertain generally to a technique ofperforming a plasma process on a processing target substrate; and, moreparticularly, the embodiments pertain to a capacitively coupled plasmaprocessing apparatus and a plasma processing method in which a highfrequency power for plasma generation is modulated in a pulse shape.

BACKGROUND ART

A capacitively coupled plasma processing apparatus includes an upperelectrode and a lower electrode arranged in parallel to each otherwithin a processing vessel. A processing target substrate (e.g., asemiconductor wafer, a glass substrate, etc) is mounted on the lowerelectrode, and a high frequency power having a frequency (typically,about 13.56 MHz or higher) suitable for plasma generation is applied tothe upper electrode or the lower electrode. Electrons are accelerated bya high frequency field generated between the two facing electrodes byapplying the high frequency power, and plasma is generated as a resultof ionization by collision between the electrons and a processing gas.Through a gas phase reaction or a surface reaction of radicals or ionsincluded in the plasma, a thin film is formed on the substrate, or amaterial or a thin film on a surface of the substrate is etched.

Recently, as a design rule is getting more miniaturized in amanufacturing process of a semiconductor device or the like, higherlevel of dimensional accuracy is required in, especially, plasmaetching. Further, it is required to increase etching selectivity againsta mask or an underlying film and to improve etching uniformity in theentire surface of a substrate. For this reason, pressure and ion energyin a processing region within a chamber tends to be reduced, and a highfrequency power having a high frequency equal to or higher than about 40MHz is used.

However, as the pressure and the ion energy are reduced, an influence ofa charging damage, which has been negligible conventionally, can be nomore neglected. That is, in a conventional plasma processing apparatushaving high ion energy, no serious problem may occur even when a plasmapotential is non-uniform in the entire surface of the substrate.However, if the ion energy is lowered at a lower pressure, thenon-uniformity of the plasma potential in the entire surface of thesubstrate may easily cause the charging damage on a gate oxide film.

To solve this problem, using a power modulation process of modulating ahigh frequency power for plasma generation in an on/off (or H level/Llevel) pulse shape is considered to be effective (Patent Document 1).According to this power modulation process, a plasma generation state inwhich plasma of a processing gas is being generated and a plasmanon-generation state in which plasma is not being generated arealternately repeated at a preset cycle during a plasma etching process.Accordingly, as compared to a typical plasma process in which plasma iscontinuously generated from the beginning of the process to the endthereof, a time period during which plasma is continuously generated maybe shortened. Accordingly, the amount of electric charges introducedinto a processing target substrate from the plasma at one time or theamount of electric charges accumulated on the surface of the processingtarget substrate may be reduced, so that the charging damage issuppressed from being generated. Therefore, a stable plasma process canbe performed and reliability of the plasma process can be improved.

Further, in the capacitively coupled plasma processing apparatus, a RFbias method is widely employed. In this RF bias method, a high frequencypower having a relatively low frequency (typically, about 13.56 MHz orlower) is applied to the lower electrode on which the substrate ismounted, and ions in the plasma are accelerated and attracted to thesubstrate by a negative bias voltage or a sheath voltage generated onthe lower electrode. In this way, by accelerating the ions in the plasmaand bringing them into collision with the surface of the substrate, asurface reaction, anisotropic etching or modification of a film may befacilitated.

However, when performing the etching process to form via holes orcontact holes by using the capacitively coupled plasma etchingapparatus, a so-called micro-loading effect may occur. That is, anetching rate may differ depending on the hole size, so that it isdifficult to control an etching depth. Especially, the etching ratetends to be higher at a large area such as a guide ring (GR), whereasthe etching rate tends to be lower at a small via in which CF-basedradicals are difficult to be introduced.

To solve this problem, a power modulation process of modulating a highfrequency power for ion attraction in a first level/second level (oron/off) pulse shape and varying the duty ratio thereof is deemed to beeffective (see, for example, Patent Document 2). According to this powermodulation process, a period of maintaining a high power of the firstlevel (H level) suitable for etching a preset film on the processingtarget substrate and a period of maintaining a low power of the secondlevel (L level) as a high frequency power for ion attraction suitablefor depositing polymer on a preset film on the processing targetsubstrate are alternately repeated at a certain cycle. Accordingly, atan area having a larger hole size, a proper polymer layer may bedeposited on the preset film at a higher deposition rate, so that theetching may be suppressed. Thus, an undesirable micro-loading effect maybe reduced, and it may be possible to perform an etching process with ahigh selectivity and a high etching rate.

Further, in the capacitively coupled plasma etching apparatus, anorganic mask having a low etching resistance, such as ArF photoresist,may be modified by applying a negative DC voltage to the upper electrodefacing the substrate with a plasma generation space therebetween andattracting secondary electrons generated in the upper electrode into asurface layer of the substrate at a high speed. Recently, in order toimprove the effect of modifying the organic mask by the high-speedelectrons, there has been proposed a method of turning on and off a highfrequency power for plasma generation with a regular pulse frequencyand, synchronously, applying a DC voltage only during a period when thehigh frequency power is off (see, for example, Patent Document 3). As inthis method, by applying the DC voltage to the upper electrode during aperiod when the high frequency power is turned off and, thus, a plasmasheath is thinned, the secondary electrons from the upper electrode mayreach the substrate efficiently, so that the organic film on thesubstrate can be enhanced.

REFERENCES

-   Patent Document 1: Japanese Patent Laid-open Publication No.    2009-071292-   Patent Document 2: Japanese Patent Laid-open Publication No.    2009-033080-   Patent Document 2: Japanese Patent Laid-open Publication No.    2010-219491

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

In the conventional capacitively coupled plasma processing apparatushaving the power modulation function as described above, both a pulsefrequency and a duty ratio (a ratio of an on-period within a singlecycle of a pulse) among plasma process recipes can be set as required.If the duty ratio is set to be low or the pulse frequency is set to behigh in the power modulation of the high frequency power for plasmageneration, it may be difficult to ignite plasma at the beginning of theprocess.

To solve this problem, conventionally, the process is started byigniting the plasma under an especially high pressure condition or ahigh RF power condition suitable for a high frequency discharge. Then,after the high frequency discharge is stabilized, the pressure or the RFpower is switched into a preset pressure or a preset RF power. In thismethod, however, since conditions different from the preset processingconditions are used for a certain time period, an adverse effect on theplasma process may be caused, so that reliability of the process may bedeteriorated.

In view of the foregoing problems, example embodiments provide a plasmaprocessing method and a plasma processing apparatus capable of stablyand securely starting a plasma process under preset processingconditions by igniting plasma securely even if a duty ratio is set to beany specific value (especially, low) or a pulse frequency is set to beany specific value (especially, high) in the power modulation process ofmodulating a high frequency power for plasma generation in a pulseshape.

Means for Solving the Problems

In one example embodiment, a plasma processing method generates plasmaby a high frequency discharge of a processing gas between a firstelectrode and a second electrode which are provided to face each otherwithin an evacuable processing vessel that accommodates therein asubstrate to be processed, which is loaded into or unloaded from theprocessing vessel, and performs a plasma process on the substrate heldon the first electrode under the plasma. The plasma processing methodincludes performing a power modulation on a first high frequency powerfor plasma generation in a pulse shape such that a first period duringwhich the first high frequency power is turned on or set to be a firstlevel and a second period during which the first high frequency power isturned off or set to be a second level lower than the first level arealternately repeated at a regular pulse frequency in the plasma process;and setting a duty ratio in the power modulation of the first highfrequency power to be an initial value for plasma ignition, and then,reducing the duty ratio from the initial value to a set value for theplasma process gradually or in a step shape during a preset transitiontime.

In another example embodiment, a plasma processing apparatus includes anevacuable processing vessel; a first electrode configured to support asubstrate to be processed within the processing vessel; a secondelectrode provided to face the first electrode within the processingvessel; a processing gas supply unit configured to supply a processinggas into the processing vessel; a first high frequency power feed unitconfigured to apply a first high frequency power to either one of thefirst electrode and the second electrode to generate plasma of theprocessing gas within the processing vessel; a modulation controllerconfigured to control the first high frequency power feed unit toperform a power modulation on the first high frequency power in a plasmaprocess such that a first period during which the first high frequencypower for plasma generation is turned on or set to be a first level anda second period during which the first high frequency power is turnedoff or set to be a second level lower than the first level arealternately repeated at a regular pulse frequency; and a duty ratiocontroller configured to set a duty ratio in the power modulation of thefirst high frequency power to be an initial value for plasma ignition,and then, reduce the duty ratio from the initial value to a preset valuefor the plasma process gradually or in a step shape during a presettransition time.

Effect of the Invention

In accordance with the plasma processing apparatus and the plasmaprocessing method of the example embodiments, it is possible to start aplasma process under preset processing conditions stably and securely byigniting plasma securely even when a duty ratio or a pulse frequency isset to be any specific value in the power modulation of modulating ahigh frequency power for plasma generation to a pulse shape.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is cross sectional view illustrating a configuration of a plasmaprocessing apparatus in accordance with a first example embodiment.

FIG. 2A is a diagram showing a first RF mode regarding various waveformsand combinations of two high frequency powers applicable to the plasmaprocessing apparatus.

FIG. 2B is a diagram showing a second RF mode in the plasma processingapparatus.

FIG. 2C is a diagram showing a third RF mode in the plasma processingapparatus.

FIG. 3A is a diagram showing a fourth RF mode in the plasma processingapparatus.

FIG. 3B is a diagram showing a fifth RF mode in the plasma processingapparatus.

FIG. 3C is a diagram showing a sixth RF mode in the plasma processingapparatus.

FIG. 3D is a diagram showing a seventh RF mode in the plasma processingapparatus.

FIG. 4A is a diagram showing a first duty ratio control method in thefourth RF mode.

FIG. 4B is a diagram showing a second duty ratio control method in thefourth RF mode.

FIG. 5A is a diagram showing a first duty ratio control method in thefifth RF mode.

FIG. 5B is a diagram showing a second duty ratio control method in thefifth RF mode.

FIG. 6 is a diagram showing a duty ratio control method in the sixth RFmode.

FIG. 7A is a diagram showing a first duty ratio control method in theseventh RF mode.

FIG. 7B is a diagram showing a second duty ratio control method in theseventh RF mode.

FIG. 8 is a diagram showing a sequence of using the second duty ratiocontrol method in the fifth RF mode when a set value of a duty ratio issmall.

FIG. 9A is a diagram showing an experiment result regarding plasmaignition property when using the second duty ratio control method in thefifth RF mode.

FIG. 9B is a diagram showing an experiment result regarding plasmaignition property when applying the first duty ratio control methodunder the processing conditions of “NG” in the above experiment usingthe second duty ratio control method.

FIG. 10A is a diagram showing another experiment result regarding plasmaignition property when using the second duty ratio control method in thefifth RF mode.

FIG. 10B is a diagram showing an experiment result regarding plasmaignition property when applying the first duty ratio control methodunder the processing conditions of “NG” in the above experiment usingthe second duty ratio control method.

FIG. 11 is a block diagram illustrating a configuration of a highfrequency power feed unit in a high frequency power system suitable forplasma generation in the example embodiment.

FIG. 12 is a block diagram illustrating a configuration of a highfrequency power feed unit for a high frequency power system suitable forion attraction in the example embodiment.

FIG. 13 is a diagram showing waveforms of components for describing anoperation of a matching device in the example embodiment.

FIG. 14 is a diagram showing waveforms of components observed in anexperimental example.

FIG. 15 is a diagram showing a duty ratio control method of acomparative example.

FIG. 16 is a diagram showing waveforms of components observed in thecomparative example.

FIG. 17 is a diagram illustrating a configuration of a plasma processingapparatus in accordance with a second example embodiment.

FIG. 18 is a diagram showing an eighth RF mode in the plasma processingapparatus.

FIG. 19 is a diagram showing a modification example of the eighth RFmode.

FIG. 20A is a diagram showing a first duty ratio control method in theeighth RF mode.

FIG. 20B is a diagram showing a second duty ratio control method in theeighth RF mode.

FIG. 21A is a diagram showing a duty ratio control method in accordancewith a modification example.

FIG. 21B is a diagram showing a duty ratio control method in accordancewith another modification example.

MODE FOR CARRYING OUT THE INVENTION

In the following, example embodiments will be described, and referenceis made to the accompanying drawings, which form a part of thedescription.

FIG. 1 is a diagram illustrating a configuration of a plasma processingapparatus in accordance with a first example embodiment. The plasmaprocessing apparatus is configured as a capacitively coupled (parallelplate type) plasma etching apparatus. By way of example, the plasmaprocessing apparatus includes a cylindrical vacuum chamber (processingvessel) 10 made of, but not limited to, aluminum having analumite-treated (anodically oxidized) surface. The chamber 10 isgrounded.

A circular columnar susceptor supporting member 14 is provided on aninsulating plate 12 such as ceramic on a bottom of the chamber 10, and asusceptor 16 made of, but not limited to, aluminum is provided on thesusceptor supporting member 14. The susceptor 16 serves as a lowerelectrode, and a processing target substrate, e.g., a semiconductorwafer W is mounted on the susceptor 16.

An electrostatic chuck 18 configured to hold the semiconductor wafer Wis provided on a top surface of the susceptor 16. The electrostaticchuck 18 includes a pair of insulating layers or insulating sheets; andan electrode 20 embedded therebetween. The electrode 20 is made of aconductive film and is electrically connected with a DC power supply 24via a switch 22. The semiconductor wafer W can be held on theelectrostatic chuck 18 by an electrostatic adsorptive force generated bya DC voltage applied from the DC power supply 24. In order to improveetching uniformity, a focus ring 26 made of, but not limited to, siliconis provided on the top surface of the susceptor 16 to surround theelectrostatic chuck 18. A cylindrical inner wall member 28 made of, butnot limited to, quartz is attached to side surfaces of the susceptor 16and the susceptor supporting member 14.

A coolant path 30 extended in, e.g., a circumferential direction isprovided within the susceptor supporting member 14. A coolant of apreset temperature, e.g., cooling water from an external chiller unit(not shown) is supplied into and circulated through the coolant path 30via pipelines 32 a and 32 b. A processing temperature of thesemiconductor wafer W on the susceptor 16 can be controlled by adjustingthe temperature of the coolant. Further, a heat transfer gas, e.g., a Hegas from a heat transfer gas supplying device (not shown) is suppliedinto a gap between a top surface of the electrostatic chuck 18 and arear surface of the semiconductor wafer W through a gas supply line 34.

Dual frequency power feed units 33 and 35 are electrically connected tothe susceptor 16. The first high frequency power feed unit 33 includes ahigh frequency power supply 36 configured to output a high frequencypower RF1 of a certain frequency f_(RF1) (e.g., about 100 MHz) suitablefor plasma generation; a high frequency transmission line 43 configuredto transmit the high frequency power RF1 outputted from the highfrequency power supply 36 to the susceptor 16; and a matching device 40provided on the high frequency transmission line 43. The second highfrequency power feed unit 35 includes a high frequency power supply 38configured to output a high frequency power RF2 of a certain frequencyf_(RF2) (e.g., about 13.56 MHz) suitable for ion attraction from plasmainto the semiconductor wafer W on the susceptor 16; a high frequencytransmission line 45 configured to transmit the high frequency power RF2outputted from the high frequency power supply 38 to the susceptor 16;and a matching device 42 provided on the high frequency transmissionline 45. A power supply conductor (e.g., a power supply rod) 44connected to a rear surface (bottom surface) of the susceptor 16 isshared by the two high frequency transmission lines 43 and 45.

An upper electrode 46 having a ground potential is provided at a ceilingof the chamber 10, facing the susceptor 16 in parallel. The upperelectrode 46 includes an electrode plate 48 having a multiple number ofgas discharge holes 48 a and made of, e.g., a silicon-containingmaterial such as Si or SiC; and an electrode supporting body 50detachably supporting the electrode plate 48 and made of a conductivematerial such as aluminum having an alumite-treated surface. A plasmageneration space or a processing space PA is formed between the upperelectrode 46 and the susceptor 16.

The electrode supporting body 50 has a gas buffer room 52 formedtherein. The electrode supporting body 50 also has, in its bottomsurface, a multiple number of gas holes 50 a extended from the gasbuffer room 52, and the gas holes 50 a communicate with the gasdischarge holes 48 a of the electrode plate 48, respectively. The gasbuffer room 52 is connected to a processing gas supply source 56 via agas supply line 54. The gas supply line 54 is provided with a mass flowcontroller (MFC) 58 and an opening/closing valve 60. If a certainprocessing gas (etching gas) is introduced into the gas buffer room 52from the processing gas supply source 56, the processing gas is thendischarged in a shower shape from the gas discharge holes 48 a of theelectrode plate 48 into the processing space PA toward the semiconductorwafer W on the susceptor 16. In this configuration, the upper electrode46 also serves as a shower head that supplies the processing gas intothe processing space PA.

Further, a passageway (not shown) in which a coolant, e.g., coolingwater flows may be provided within the electrode supporting body 50. Theentire upper electrode 46, especially, the electrode plate 48 iscontrolled to a preset temperature through the coolant by an externalchiller unit. Further, in order to stabilize the temperature controlover the upper electrode 46, a heater (not shown) including a resistanceheating device may be provided within or on a top surface of theelectrode supporting body 50.

An annular space formed between a sidewall of the chamber 10, and thesusceptor 16 and the susceptor supporting member 14 serves as a gasexhaust space, and a gas exhaust opening 62 of the chamber 10 is formedin a bottom of this gas exhaust space. The gas exhaust opening 62 isconnected to a gas exhaust device 66 via a gas exhaust line 64. The gasexhaust device 66 includes a vacuum pump such as a turbo molecular pumpand is configured to depressurize the inside of the chamber 10,particularly, the processing space PA to a required vacuum level.Further, a gate valve 70 configured to open and close aloading/unloading opening 68 for the semiconductor wafer W is providedat the sidewall of the chamber 10.

A main controller 72 includes one or more microcomputers and isconfigured to control an overall operation (sequence) of the apparatusand individual operations of respective components within the apparatus,particularly, the high frequency power supplies 36 and 38, the matchingdevices 40 and 42, the MFC 58, the opening/closing valve 60, the gasexhaust device 66, etc., according to software (program) and recipesstored in an external memory or an internal memory.

Further, the main controller 72 is connected to a man-machine interfacemanipulation panel (not shown) including an input device such as akeyboard and a display device such as a liquid crystal display and,also, connected to an external storage device (not shown) that storesvarious types of data such as various programs or recipes, settingvalues, etc. In the present example embodiment, the main controller 72is configured as a single control unit. However, it may be also possibleto adopt a configuration in which multiple control units divide up thefunctions of the main controller 72 individually or hierarchically.

A basic operation of single-sheet typed dry etching in the capacitivelycoupled plasma etching apparatus configured as described above isperformed as follows. First, the gate valve 70 is opened, and asemiconductor wafer W to be processed is loaded into the chamber 10 andmounted on the electrostatic chuck 18. Then, a processing gas, i.e., anetching gas (generally, a gaseous mixture) is introduced into thechamber 10 from the processing gas supply source 56 at a preset flowrate and a preset flow rate ratio, and the inside of the chamber 10 isevacuated to be a set vacuum pressure by the gas exhaust device 66.Further, a high frequency power RF1 (about 100 MHz) from the highfrequency power supply 36 and a high frequency power RF2 (about 13.56MHz) from the high frequency power supply 38 are applied to thesusceptor 16, overlapped with each other (or separately). Further, a DCvoltage from the DC power supply 24 is applied to the electrode 20 ofthe electrostatic chuck 18, so that the semiconductor wafer W is held onthe electrostatic chuck 18. The etching gas discharged from the upperelectrode 46 serving as the shower head is discharged under a highfrequency electric field between the two electrodes 46 and 16, so thatplasma is generated in the processing space PA. An etching target filmon a main surface of the semiconductor wafer W is etched by radicals orions included in the plasma.

In the capacitively coupled plasma etching apparatus, as for the kinds,forms, and combinations of the high frequency powers applied to thesusceptor 16 within the chamber 10, the following seven types of RFmodes may be selectively used under the control of the main controller72 upon the high frequency power feed units 33 and 35. Among the seventypes of RF modes, in a first RF mode to a third RF mode, the powermodulation is not used, whereas in a fourth RF mode to a seventh RFmode, the power modulation is used.

As depicted in FIG. 2A, the first RF mode is of a typical dual frequencyapplication type that applies dual frequency powers to the lowerelectrode. In this first RF mode, the high frequency power RF1 of afrequency (e.g., about 100 MHz) in the high frequency power feed unit 33is set as a continuous wave CW of a constant power, and the highfrequency power RF2 of a frequency (e.g., about 13.56 MHz) in the highfrequency power feed unit 35 is set as a continuous wave CW of aconstant power. In this case, the high frequency power RF1 maydominantly work for or contribute to plasma generation, whereas the highfrequency power RF2 may dominantly work for or contribute to ionattraction from the plasma into the semiconductor wafer W on thesusceptor 16.

As depicted in FIG. 2B, in the second RF mode, the high frequency powerRF1 of the high frequency power feed unit 33 is set as a continuous waveCW of a constant power, and the high frequency power RF2 of the highfrequency power feed unit 35 is maintained off constantly. In this case,the high frequency power RF1 may not only work for plasma generation butalso work for ion attraction, though the effect on the ion attraction isnot as high as that of the high frequency power RF2.

Referring to FIG. 2C, in the third RF mode, the high frequency power RF1of the high frequency power feed unit 33 is maintained off constantly,and the high frequency power RF2 of the high frequency power feed unit35 is set as a continuous wave CW of a constant power. In this case, thehigh frequency power RF2 may not only work for ion attraction but alsowork for plasma generation, though the effect on the electric dischargeis not as high as that of the high frequency power RF1.

FIG. 3A depicts the fourth RF mode. In the fourth RF mode, the highfrequency power RF1 of the high frequency power feed unit 33 is set tohave a pulse waveform through power modulation, and the high frequencypower RF2 of the high frequency power feed unit 35 is set as acontinuous wave CW of a constant power. In this case, the high frequencypower RF1 may dominantly work for plasma generation, whereas the highfrequency power RF2 may dominantly work for ion attraction.

Referring to FIG. 3B, in the fifth RF mode, the high frequency power RF1of the high frequency power feed unit 33 is set to have a pulse waveformthrough power modulation, and the high frequency power RF2 of the highfrequency power feed unit 35 is maintained off constantly. In this case,the high frequency power RF1 may not only work for plasma generation butalso work for ion attraction, through the effect on the ion attractionis not as high as that of the high frequency power RF2.

Referring to FIG. 3C, in the sixth RF mode, the high frequency power RF1of the high frequency power feed unit 33 is set as a continuous wave CWof a constant power, and the high frequency power RF2 of the highfrequency power feed unit 35 is set to have a pulse waveform throughpower modulation. In this case, the high frequency power RF1 maydominantly work for plasma generation, whereas the high frequency powerRF2 may dominantly work for ion attraction.

Lastly, in the seventh RF mode as depicted in FIG. 3D, the highfrequency power RF1 of the high frequency power feed unit 33 ismaintained off constantly, and the high frequency power RF2 of the highfrequency power feed unit 35 is set to have a pulse waveform throughpower modulation. In this case, the high frequency power RF2 may notonly work for ion attraction but also work for plasma generation,through the effect on the electric discharge is not as high as that ofthe high frequency power RF1.

In the power modulation according to the present example embodiment, asshown in FIG. 3A to FIG. 3D, an on-period (first period) T_(on) duringwhich the high frequency power RF1 (RF2) is maintained on and anoff-period (second period) T_(off) during which the high frequency powerRF1 (RF2) is maintained off are alternately repeated at a regular pulsefrequency or cycle T_(C). The RF power during the on-period is set to beconstant. The main controller 72 may output a modulation control pulsesignal PS for determining a pulse frequency and a duty ratio of powermodulation to the high frequency power supply 36 (38). Here, if setvalues of the pulse frequency and the duty ratio are defined as f, andD_(S), respectively, equations of T_(C)=1/f_(S), T_(C)=T_(on)+T_(off),D_(S)=T_(on)/(T_(on)+T_(off)) are established.

(Duty Ratio Control Method for Power Modulation in First ExampleEmbodiment)

Now, referring to FIG. 4A to FIG. 7B, a duty ratio control of the powermodulation in the fourth RF mode to the seventh RF mode will bediscussed. The duty ratio control may be performed as one of controloperations performed by the main controller 72 upon the high frequencypower feed units 33 and 35 based on the recipes or other conditions setthrough the manipulation panel, for example. That is, in the firstexample embodiment, the main controller 72 serves as a duty ratiocontrol unit.

In the fourth RF mode (FIG. 3A), two types of duty ratio control methods[4RFM-1, 4RFM-2] may be selectively used. As shown in FIG. 4A and FIG.4B, in the fourth RF mode, when starting a process, the high frequencypower RF1 (high frequency power feed unit 33) for plasma generation isfirst driven at a time point t₀. Then, at a time point T₁ after a lapseof a certain time T_(a), the high frequency power RF2 (high frequencypower feed unit 35) for ion attraction is driven. Desirably, the elapsedtime T_(a) may be set to be of a value (e.g., about 0.4 sec to about 0.8sec) larger than a time (typically, about 0.2 sec to about 0.5 sec)taken before plasma is ignited after the application of the highfrequency power RF1 is started.

Here, in the first duty ratio control method [4RFM-1], as shown in FIG.4A, at the time point T₀ when starting the process, a duty ratio of thehigh frequency power RF1 to which the power modulation is performed isset to be an initial value (in this experimental example, about 90%)which allows plasma to be ignited securely under any power modulatingconditions (particularly, a duty ratio and a pulse frequency). It may bedesirable that the initial value is as close to an originally set valueD_(S) of the duty ratio for the etching process as possible. That is,desirably, the initial value may be a value (typically, about 85% toabout 95%) close to a lower limit within a duty ratio range in whichplasma can be ignited securely under the power modulating conditions.

At the substantially same time of starting the process, the duty ratioof the high frequency power RF1 is gradually reduced from the initialvalue (about 90%) in a regular negative gradient or in a ramp waveform.At a time point t₂ after a lapse of a preset time T_(d) (T_(d)>T_(a)),the duty ratio has the originally set value D_(s) for the etchingprocess. After the time point t₂, the duty ratio is fixed or maintainedat the set value D_(s) until the end (time point T₄) of the process.Further, when using the high frequency powers RF1 and RF2 in combination(i.e., when applying them while overlapping them), the high frequencypower RF2 for ion attraction is stopped (at a time point t₃) slightlybefore the end of the process. This first duty ratio control method[4RFM-1] may be effective when plasma is difficult to be ignited in thefourth RF mode, e.g., when the duty ratio D_(s) is set to be low or apulse frequency f_(s) is set to be high.

In the second duty ratio control method [4RFM-2], the duty ratio of thehigh frequency power RF1 has the originally set value D_(s) from thebeginning (t₀) of the process to the end (t₄) of the process, as shownin FIG. 4B. This duty ratio control method [4RFM-2] may be appropriatelyused in case that it is possible to ignite plasma securely under theduty ratio D_(s) and the pulse frequency f_(s) of the power modulationperformed in the etching process.

In the fifth RF mode (FIG. 3B), two types of duty ratio control methods[5RFM-1, 5RFM-2] may be selectively used. As shown in FIG. 5A and FIG.5B, in the fifth RF mode, when the process is started, the highfrequency power RF1 (high frequency power feed unit 33) for both plasmageneration and ion attraction is first driven at a time point t₀.

Here, the first duty ratio control method [5RFM-1] has the same sequenceas that of the first duty ratio control method [4RFM-1] in theabove-described fourth RF mode. That is, as shown in FIG. 5A, at a timepoint T₀ when starting the process, a duty ratio of the high frequencypower RF1 to which the power modulation is performed is set to be aninitial value (in this experimental example, about 90%) which allowsplasma to be ignited securely under any power modulating conditions(particularly, a duty ratio and a pulse frequency). Then, at thesubstantially same time of starting the process, the duty ratio of thehigh frequency power RF1 is gradually reduced from the initial value(about 90%) in a regular negative gradient or in a ramp waveform. At atime point t₂ after a lapse of a preset time T_(d), the duty ratio hasan originally set value D_(s) for the etching process. After the timepoint t₂, the duty ratio of the high frequency power RF1 is fixed at theset value D_(s) until the end (time point T₄) of the process. This firstduty ratio control method [5RFM-1] may be effective when plasma isdifficult to be ignited in the fifth RF mode, for example, when the dutyratio D_(s) is set to be low or a pulse frequency f_(s) is set to behigh.

The second duty ratio control method [5RFM-2] in the fifth RF mode hasthe same sequence as that of the second duty ratio control method[4RFM-2] in the fourth RF mode. That is, as depicted in FIG. 5B, theduty ratio of the high frequency power RF1 has the originally set valueD_(s) from the beginning (t₀) of the process to the end (t₄) of theprocess. This duty ratio control method [5RFM-2] may be appropriatelyused when it is possible to ignite plasma securely under the duty ratioD_(s) and the pulse frequency f_(s) of the power modulation performed inthe etching process.

In the sixth RF mode (FIG. 3C), a single kind of duty ratio controlmethod is used. As shown in FIG. 6, in the sixth RF mode, when startingthe process, the high frequency power RF1 (high frequency power feedunit 33) for plasma generation is first driven at a time point t₀, andthe high frequency power RF2 (high frequency power feed unit 35) for ionattraction is driven at a time point t₁ after a lapse of a certain timeT_(a). In this case, since the high frequency power RF1 is a continuouswave CW having a duty ratio equivalent to about 100%, plasma may besecurely ignited within the chamber 10 regardless of the values of theduty ratio D_(s) and the pulse frequency f_(s) of the power modulationon the high frequency power RF2, as long as a pressure or a power of RF1is set to be a typical value.

Accordingly, in the duty ratio control method of the sixth RF mode, theduty ratio of the high frequency power RF2 has the set value D_(s) fromthe time point t₁ when driving the high frequency power RF2 (highfrequency power feed unit 35) to the end (t₃) of the process.

In the seventh RF mode (FIG. 3D), two types of duty ratio controlmethods [7RFM-1, 7RFM-2] may be selectively used. In the seventh RFmode, as shown in FIG. 7A and FIG. 7B, when starting a process, the highfrequency power RF2 (high frequency power feed unit 35) for both plasmageneration and ion attraction is driven at a time point t₀.

Here, in the first duty ratio control method [7RFM-1], as depicted inFIG. 7A, at a time point T₀ when starting the process, a duty ratio ofthe high frequency power RF2 to which the power modulation is performedis set to be an initial value (in this experimental example, about 90%)which allows plasma to be ignited securely under any power modulatingconditions (particularly, a duty ratio and a pulse frequency). Then,immediately after the process is started, the duty ratio of the highfrequency power RF2 is gradually reduced from the initial value (about90%) in a regular negative gradient or in a ramp waveform. At a timepoint t₂ after a lapse of a preset time T_(d), the duty ratio has theoriginally set value D_(s) for the etching process. After the time pointt₂, the duty ratio is fixed at the set value D_(s) until the end (timepoint T₄) of the process. This first duty ratio control method [7RFM-1]may be appropriately used when plasma is difficult to be ignited in theseventh RF mode, for example, when the duty ratio D_(s) is set to be lowor a pulse frequency f_(s) is set to be high.

In the second duty ratio control method [7RFM-2] in the seventh RF mode,as depicted in FIG. 7B, a duty ratio of the high frequency power RF1 hasthe originally set value D_(s) from the beginning (t₀) of the process tothe end (t₄) of the process. This duty ratio control method [7RFM-2] maybe appropriately used in case that it is possible to ignite plasmasecurely under the duty ratio D_(s) and the pulse frequency f_(s) of thepower modulation performed in the etching process.

As described above, in the first example embodiment, when it isdifficult to ignite plasma in the fourth RF mode, the fifth RF mode, andthe seventh RF mode, the duty ratio of the power modulation is set to bethe initial value (about 90%) for plasma ignition when starting theprocess, as illustrated in FIG. 4A, FIG. 5A and FIG. 7A. Then, duringthe transition time T_(d), the duty ratio is gradually reduced from theinitial value to the set value D_(s) for the etching process in a rampwaveform. Here, if the transition time T_(d) is too short, a matchingoperation within the matching device 40 (42) may become unstable,whereas if the transition time T_(d) is too long, it may affect aprocess characteristic or a process result of the etching process.Typically, in consideration of such limits in the transition time T_(d),the transition time T_(d) may be set to be in the range from, e.g.,about 0.5 sec to about 3.0 sec.

(Effect on Plasma Ignition Property in First Example Embodiment)

Now, according to the first example embodiment, a verificationexperiment for investigating an effect on plasma ignition of the firstduty ratio control method [5RFM-1] in the fifth RF mode will beexplained.

The present inventors conduct a plasma etching experiment using thefifth RF mode. Major processing conditions are as follows: a chamberinternal pressure is set to be, e.g., about 2666 Pa (about 20 mTorr); aRF1 power and a RF2 power are set to be, e.g., about 300 W and about 0W, respectively; C₄F₈/O₂/Ar (about 24 sccm/about 16 sccm/about 150 sccm)are used as an etching gas; and a gap between the electrodes is set tobe, e.g., about 22 mm. In this experiment, the second duty ratio controlmethod [5RFM-2] is used, and a duty ratio D_(s) and a pulse frequencyf_(s) of the pulse modulation performed on a high frequency power RF1are varied as parameters in the range from, e.g., about 10% to about 90%and in the range from, e.g., about 5 kHz to about 90 kHz, respectively.Then, plasma ignition properties in respective combinations of theparameter values (D_(s), f_(s)) are evaluated. FIG. 8 illustrates asequence when using the second duty ratio control method [5RFM-2] byselecting a low value (e.g., about 10%) as the set value of the dutyratio D_(s).

FIG. 9A depicts an experimental result of using the second duty ratiocontrol method [5RFM-2]. On a table (matrix) in this figure, cells inrows indicate parameter values of the set value of the duty ratio D_(s),and cells in columns indicate parameter values of the pulse frequencyf_(s). A notation of “OK” implies that plasma is ignited and maintainedstably in a process using parameter values (f_(s), D_(s)) correspondingto a certain cell. Meanwhile, a notation of “NG” means that plasma isnot ignited or is not stable though ignited in a process using parameter(f_(s), D_(s)) corresponding to a certain cell. Further, a blank impliesthat an experiment for a process using parameter values (f_(s), D_(s))corresponding to a certain cell is not conducted.

As shown in this figure, experimental results of “NG” (meaning thatplasma is not ignited or is not stable) are obtained when parametervalues (f_(s), D_(s)) are (about 40 kHz, about 40%), (about 40 kHz,about 50%), (about 40 kHz, about 60%), (about 40 kHz, about 70%), (about40 kHz, about 80%), (about 50 kHz, about 70%), (about 50 kHz, about80%), (about 60 kHz, about 60%), (about 60 kHz, about 70%), and (about70 kHz, about 70%). In all of the other combinations of parameter values(f_(s), D_(s)), experimental results of “OK” (meaning that plasma isignited and is stable) are obtained.

For each of the parameter values (f_(s), D_(s)) in the cases where theexperimental results of “NG” are obtained under the second duty ratiocontrol method [5RFM-2], the present inventors conduct a plasma etchingexperiment by using the first duty ratio control method [5RFM-1] underthe same processing conditions as specified above. Then, plasma ignitionproperty is evaluated.

As a result, as shown in FIG. 9B, experimental results of “OK” (meaningthat plasma is ignited and is stable) are obtained in all of cases wherethe parameter values (f_(s), D_(s)) are set to be (about 40 kHz, about40%), (about 40 kHz, about 50%), (about 40 kHz, about 60%), (about 40kHz, about 70%), (about 40 kHz, about 80%), (about 50 kHz, about 70%),(about 50 kHz, about 80%), (about 60 kHz, about 60%), (about 60 kHz,about 70%), and (about 70 kHz, about 70%).

Further, in this experiment, the transition time T_(d) is set to beabout 1.0 sec in all of the above cases. A notation of “1.0 s” in FIG.9B indicates this setting of the transition time. Further, a notation of“OK” in FIG. 9B has the same meaning as in FIG. 9A. That is, thenotation of “OK” implies that an experimental result of “OK” is obtainedunder the second duty ratio control method [5RFM-2] in a process usingparameter values (f_(s), D_(s)) corresponding to a certain cell.

Further, the present inventors also conduct another experiment forplasma etching using the fifth RF mode. In this another experiment,conditions of the chamber internal pressure, the RF1/RF2 powers and theetching gas are set to be the same as those of the aforementionedexperiment, but a gap between the electrodes is changed to be, e.g.,about 30 mm. As in the aforementioned experiment, the second duty ratiocontrol method [5RFM-2] is used, and the duty ratio D_(s) and the pulsefrequency f_(s) of the pulse modulation performed on the high frequencypower RF1 are varied as parameters in the range from, e.g., about 10% toabout 90% and in the range from, e.g., about 5 kHz to about 90 kHz,respectively. Then, the plasma ignition properties in respectivecombinations of the parameter values (f_(s), D_(s)) are evaluated.

As a result, as depicted in FIG. 10A, when parameter values (f_(s),D_(s)) are set to be (about 5 kHz, about 10%), (about 5 kHz, about 20%),(about 10 kHz, about 10%), (about 20 kHz, about 20%), (about 20 kHz,about 30%), (about 20 kHz, about 40%), (about 20 kHz, about 50%) and(about 30 kHz, about 30%), experimental results are “NG.” In all of theother combinations of parameter values (f_(s), D_(s)), “OK” areobtained.

Based on the experimental results, for each of the parameter values(f_(s), D_(s)) when the experimental results of “NG” are obtained underthe second duty ratio control method [5RFM-2], the present inventorsconduct a plasma etching experiment by using the first duty ratiocontrol method [5RFM-1] under the same processing conditions asspecified above. Then, plasma ignition property is evaluated.

As a result, as shown in FIG. 10B, experimental results of “OK” (meaningthat plasma is ignited and is stable) are obtained in all of cases whenparameter values (f_(s), D_(s)) are set to be (about 5 kHz, about 10%),(about 5 kHz, about 20%), (about 10 kHz, about 10%), (about 20 kHz,about 20%), (about 20 kHz, about 30%), (about 20 kHz, about 40%), (about20 kHz, about 50%) and (about 30 kHz, about 30%).

Further, in this experiment, the transition time T_(d) is set to beabout 2.5 sec when the parameter values (f_(s), D_(s)) are (about 5 kHz,about 10%) and (about 5 kHz, about 20%); about 1.5 sec, when theparameter values (f_(s), D_(s)) are (about 10 kHz, about 10%); and about1.0 sec, when the parameter values (f_(s), D_(s)) are (about 20 kHz,about 20%), (about 20 kHz, about 30%), (about 20 kHz, about 40%), (about20 kHz, about 40%) and (about 30 kHz, about 30%). Notations of “2.5 s,”“1.5 s,” and “1.0 s” in FIG. 10B indicate these setting of thetransition time. Further, in FIG. 10B, a notation of “OK” implies thatan experimental result of “OK” is obtained under the second duty ratiocontrol method [5RFM-2] in a process using parameter values (f_(s),D_(s)) corresponding to a certain cell.

As stated above, in the above-described fifth RF mode, when it ispossible to ignite plasma securely under the second duty ratio controlmethod [5RFM-2], it may be desirable to use the second duty ratiocontrol method [5RFM-2] in which the duty ratio of the power modulationis fixed at the set value D_(s) from the beginning of the process.However, when it is difficult to ignite plasma securely under the secondduty ratio control method [5RFM-2], it may be desirable to use the firstduty ratio control method [5RFM-1] in which the duty ratio of the powermodulation is reduced in a ramp waveform immediately after the processis started, in order to perform a plasma process stably and securelyunder desired processing conditions.

Likewise, in the above-described fourth RF mode, when it is possible toignite plasma securely under the second duty ratio control method[4RFM-2], it may be desirable to use the second duty ratio controlmethod [4RFM-2] in which the duty ratio of the power modulation is fixedat the set value D_(s) from the beginning of the process. However, whenit is difficult to ignite plasma securely under the second duty ratiocontrol method [4RFM-2], it may be desirable to use the first duty ratiocontrol method [4RFM-1] in which the duty ratio of the power modulationis reduced in a ramp waveform immediately after starting the process inorder to perform a plasma process stably and securely under desiredprocessing conditions.

Furthermore, in the above-described seventh RF mode as well, when it ispossible to ignite plasma securely under the second duty ratio controlmethod [7RFM-2], it may be desirable to use the second duty ratiocontrol method [7RFM-2] in which the duty ratio of the power modulationis fixed at the set value D_(s) from the beginning of the process.However, when it is difficult to ignite plasma securely under the secondduty ratio control method [7RFM-2], it may be desirable to use the firstduty ratio control method [7RFM-1] in which the duty ratio of the powermodulation is reduced in a ramp waveform immediately after starting theprocess in order to perform a plasma process stably and securely underdesired processing conditions.

(Configuration and Operation of High Frequency Power Feed Unit in FirstExample Embodiment)

FIG. 11 illustrates a configuration of the high frequency power feedunit 33, particularly, the high frequency power supply 36 and thematching device 40 in accordance with the first example embodiment.

The high frequency power supply 36 includes an oscillator 80A configuredto generate a sine wave of a frequency (e.g., about 100 MHz) suitablefor plasma generation; a power amplifier 82A configured to amplify apower of the sine wave outputted from the 80A with a variable gain oramplification factor; and a power supply controller 84A configured tocontrol the oscillator 80A and the power amplifier 82A directly inresponse to a control signal from the main controller 72. Not only thepulse signal PS for the modulation control but typical control signalsfor power on/off or power interlock relationship and data such as powersetting values are also inputted from the main controller 72 to thepower supply controller 84A. The main controller 72 and the power supplycontroller 84A constitute a power modulation unit of a high frequencypower RF1 system.

Within the high frequency power supply 36, a RF power monitor 86A isalso included. The RF power monitor 86A may include, though notillustrated, a directional coupler, a progressive wave power monitor anda reflection wave power monitor. Here, the directional coupler extractssignals corresponding to a RF power (progressive wave) propagating onthe high frequency transmission line 43 in a forward direction and a RFpower (reflection wave) propagating on the high frequency transmissionline 43 in a backward direction. The progressive power monitor isconfigured to output a signal indicating a power of a fundamentalfrequency progressive wave (about 100 MHz) included in the progressivewave propagating on the high frequency transmission line 43 based on theprogressive wave power detection signal extracted by the directionalcoupler. This signal, i.e., a fundamental frequency progressive wavepower measurement value is sent to the power supply controller 84Awithin the high frequency power supply 36 for power feedback control andalso sent to the main controller 72 for monitor display. The reflectionwave power monitor is configured to measure a power of a fundamentalfrequency reflection wave (about 100 MHz) included in the reflectionwave returning back to the high frequency power supply 36 from plasmawithin the chamber 10 and, also, to measure a total power of allreflection wave spectra included in the reflection wave returned back tothe high frequency power supply 36 from the plasma within the chamber10. A fundamental frequency reflection wave power measurement valueoutputted by the reflection wave power monitor is sent to the maincontroller 72 for monitor display, and a total reflection wave powermeasurement value is sent to the power supply controller 84A within thehigh frequency power supply 36 as a monitoring value for protecting thepower amplifier.

The matching device 40 includes a matching circuit 88A having a multiplenumber of, e.g., two variable reactance elements (e.g., variablecapacitors or variable reactors) X_(H1) and X_(H2); a matchingcontroller 94A configured to vary reactance of the variable reactanceelements X_(H1) and X_(H2) via actuators such as stepping motors (M) 90Aand 92A; and an impedance sensor 96A configured to measure loadimpedance including impedance of the matching circuit 88A on the highfrequency power feed line 43.

The matching controller 94A is operated under the control of the maincontroller 72. The matching controller 94A is configured to vary thereactance of the variable reactance elements X_(H1) and X_(H2) bycontrolling the motors 90A and 92A such that a measurement value of theload impedance measured by the impedance sensor 96A may be equal to orapproximate to a matching point (typically, about 50Ω) corresponding tothe impedance on the side of the high frequency power supply 36.

The impedance sensor 96A includes, though not shown, a RF voltagedetector and a RF current detector; and a load impedance measurementvalue calculating unit. The RF voltage detector and the RF currentdetector are configured to detect a RF voltage and a RF current on thehigh frequency transmission line 43, respectively. Further, the loadimpedance measurement value calculating unit is configured to calculatea measurement value of the load impedance from the RF voltage value andthe RF current value detected by the RF voltage detector and the RFcurrent detector, respectively.

In this first example embodiment, as shown in FIG. 13, when performingthe power modulation on the high frequency power RF1, a monitoringsignal AS designating a monitoring time (load impedance measuring time)T_(H) included in an on-period T_(on) for each cycle of the pulsefrequency is sent from the main controller 72 to the impedance sensor96A. Desirably, as depicted in FIG. 13, the monitoring time T_(H) is setwithin a time range excluding transition times T_(A1) and T_(A2)immediately after and immediately before the on-period T_(on). Here,during the transition times T_(A1) and T_(A2), a RF1-based reflectionwave power increases abruptly on the high frequency transmission line43. Further, the monitoring time T_(H) is set within the on-periodT_(on), not within an off-period T_(off) even if the high frequencypower RF1 is on/off by the pulse frequency f_(s). Thus, from thematching device 40, the high frequency power RF1 seems to be acontinuous wave CW which is kept on.

The impedance sensor 96A measures the load impedance during themonitoring time T_(H) which is controlled by the monitoring signal AS.Accordingly, the measurement value of the load impedance sent to thematching controller 94A from the impedance sensor 96A is updated foreach cycle of the pulse frequency f_(s) in synchronization with thepower modulation. Even during this updating operation, the matchingcontroller 94A does not stop the matching operation, i.e., the controlof varying the reactance of the reactance elements X_(H1) and X_(H2),and drives the stepping motors 90A and 92A continuously such that loadimpedance measurement value immediately before updating operation can beequal to or approximate to the matching point.

In this example embodiment, the main controller 72 serves as amonitoring time controller for the matching device 40 and controls themonitoring time T_(H) in proportion to a variation in the duty ratio inthe power modulation of the high frequency power RF1. That is, asdepicted in FIG. 13, when the duty ratio of the power modulation isreduced gradually immediately after the process is started, themonitoring time T_(H) is also gradually reduced in proportion.

FIG. 12 illustrates a configuration of the high frequency power feedunit 35 in accordance with the first example embodiment. The highfrequency power supply 38 and the matching device 42 of the highfrequency power feed unit 35 have the same configurations and functionsas those of the high frequency power supply 36 and the matching device40 of the above-described high frequency power feed unit 33 except thata frequency (e.g., about 13.56 MHz) of the high frequency power RF2 usedin the high frequency power feed unit 35 is different from the frequency(e.g., about 100 MHz) of the high frequency power RF1. That is, exceptthat an oscillator 80B of the high frequency power supply 38 generates asine wave having a frequency (e.g., about 13.56 MHz) suitable for ionattraction, respective components within the high frequency power supply38 and the matching device 42 have the same configurations and functionsas those of corresponding components within the high frequency powersupply 36 and the matching device 40. By way of example, a power supplycontroller 84B and the main controller 72 constitute a power modulationunit of the high frequency power RF2 system.

Here, a modulation control pulse signal PS and a monitoring signal BSare respectively sent from the main controller 72 to the power supplycontroller 84B within the high frequency power supply 38 and animpedance sensor 96B within the matching device 42 of the high frequencypower supply 38, independently from the signals for the high frequencypower feed unit 33.

That is, when performing the power modulation on the high frequencypower RF2, as depicted in FIG. 13, a monitoring signal BS designating amonitoring time (load impedance measuring time) T_(L) included in anon-period T_(on) for each cycle of the pulse frequency is sent from themain controller 72 to the impedance sensor 96B. Desirably, as depictedin FIG. 13, the monitoring time T_(L) is set within a time rangeexcluding transition times T_(B1) and T_(B2) immediately after andimmediately before the on-period T_(on). Here, during the transitiontimes T_(B1) and T_(B2) a RF2-based reflection wave power increasesabruptly on the high frequency transmission line 45. Further, themonitoring time T_(L) is set within the on-period T_(on), not within anoff-period T_(off) even if the high frequency power RF2 is on/off by thepulse frequency f_(s). Thus, from the matching device 42, the highfrequency power RF2 seems to be a continuous wave CW which is kept on.

The impedance sensor 96B measures the load impedance during themonitoring time T_(L) which is controlled by the monitoring signal BS.Accordingly, a measurement value of the load impedance sent to thematching controller 94B from the impedance sensor 96B is updated foreach cycle of the pulse frequency f_(s) in synchronization with thepower modulation. Even during this updating operation, the matchingcontroller 94B does not stop a matching operation, i.e., a control ofvarying reactance of reactance elements X_(L1) and X_(L2) and drivesstepping motors 90B and 92B continuously such that a load impedancemeasurement value immediately before updating operation can be equal toor approximate to the matching point.

The main controller 72 serves as a monitoring time controller for thematching device 42 and controls the monitoring time T_(L) in proportionto a duty ratio in the power modulation of the high frequency power RF2.That is, as depicted in FIG. 13, when the duty ratio of the powermodulation is reduced gradually immediately after the process isstarted, the monitoring time T_(L) is also gradually reduced inproportion.

Regarding the matching operation, the present inventors investigateeffects on the first duty ratio control method [5RFM-1] (FIG. 5A) in thefifth RF mode and the monitoring time control method (FIG. 13) throughthe plasma etching experiment conducted under the same processingconditions as specified above. In this experiment, variable capacitorsRF₁C₁ and RF₁C₂ are used as the two variable reactance elements X_(H1)and X_(H2) included in the matching circuit 88A of the matching device40, respectively.

FIG. 14 shows waveforms of the respective components observed in theexperiment of this experimental example. As shown in the figure, a step(capacitance position) of the variable capacitor RF₁C₁ is overshot froman initial value immediately after a process is started. Then, the step(capacitance position) stabilized during a transition time T_(d) (e.g.,about 2.5 sec) in the RF₁C₁ is maintained substantially constantafterwards even after a duty ratio is fixed at a set value D_(s) (e.g.,about 30%). Further, a step (capacitance position) of the variablecapacitor RF₁C₂ decreases from an initial value in a step shapeimmediately after the process is started. Then, the step (capacitanceposition) of the RF₁C₂ stabilized during the transition time T_(d) ismaintained substantially constant afterwards even after a duty ratio isfixed at the set value D_(s) (e.g., about 30%). A reflection wave powerRF₁P_(r) on the high frequency transmission line 43 is impulsivelygenerated immediately after the process is started, but it stops duringthe transition time T_(d) and almost no reflection wave power isgenerated thereafter. As stated, in this experimental example, it isobserved that impedance matching is achieved on the high frequencytransmission line 43 from the mid of the transition time T_(d) until theend of the process.

As a comparative example, as shown in FIG. 15, the present inventorsalso conduct a plasma etching experiment under the same processingconditions as those of the above-described experimental example by usinga duty ratio control method in which a high frequency power RF1 is setas a continuous wave (duty ratio of about 100%) during a starting timeT_(e) (e.g., about 2.5 sec) corresponding to the transition time T_(d)of the experimental example immediately after the process is started,and the power modulation of the set duty ratio D_(s) (e.g., about 30%)is performed on the high frequency power RF1 after the lapse of thestarting time T_(e).

FIG. 16 shows waveforms of the respective components observed in thiscomparative example. As shown in the figure, the waveforms of therespective components during the starting time T_(e) are mostly the sameas those of the experimental example. Further, in this comparativeexample, the monitoring signal AS (designating the monitoring time T_(H)within the on-period T_(on) for each cycle of the pulse frequency),which is the same as that in the experimental example, is sent from themain controller 72 to the impedance sensor 96A of the matching device40. However, waveforms of the respective components after the startingtime T_(e), i.e., after the high frequency power RF1 is switched to apulse of the power modulation from the continuous wave CW (after a timepoint t₂) are totally different from those of the experimental example,except for a progressive wave power RF₁P_(t) on the high frequencytransmission line 43.

That is, the step (capacitance position) of the variable capacitor RF₁C₁is returned to an initial value immediately after the high frequencypower RF1 is switched to the pulse of the power modulation (i.e.,immediately after the time point t₂), and great hunting occurscontinuously until the end of the process. Further, the step(capacitance position) of the variable capacitor RF₁C₂ is also returnedto an initial value immediately after the high frequency power RF1 isswitched to the pulse of the power modulation (i.e., immediately afterthe time point t₂), and hunting occurs continuously until the end of theprocess, though the degree of the hunting is not as great as that of thevariable capacitor RF₁C₁. Meanwhile, the reflection wave power RF₁P_(r)on the high frequency transmission line 43 is found to be increasedgreatly in a step shape immediately after the high frequency power RF1is switched to the pulse of the power modulation (i.e., immediatelyafter the time point t₂) and does not decrease until the end of theprocess. As stated above, in the comparative example, even though amatching monitoring method of limiting a monitoring time of theimpedance sensor to within an on-period of each cycle of the pulsefrequency, it is found out that impedance matching is not achieved atall on the high frequency transmission line 43 until the end of theprocess after the high frequency power RF1 is switched to the pulse ofthe power modulation from the continuous wave CW.

Further, in the comparative example, such a failure in the matchingoperation (FIG. 16) may occur when the plasma load impedance is greatlydifferent between the two cases when the first high frequency power isthe continuous wave CW and the first high frequency power is under thepower modulation. Mostly, the failure in the matching operation may behighly likely to occur when the duty ratio of the power modulation islow. However, even if the duty ratio is low, if a difference (variation)in the plasma load impedance is small due to other conditions such as apressure, such a failure in the matching operation may be avoided. Inany cases, it may be possible to solve the problem of matching failurein, e.g., the comparative example, by using the duty ratio controlmethod in accordance with the example embodiment.

(Configuration and Operation of Plasma Processing Apparatus in SecondExample Embodiment)

FIG. 17 illustrates a configuration of a plasma processing apparatus inaccordance with a second example embodiment. In this figure, partshaving the same configurations as or similar functions to those of theplasma processing apparatus (FIG. 1) of the first example embodimentwill be assigned the same reference numerals as those in the firstexample embodiment.

In the second example embodiment, a DC power supply unit 100 configuredto apply a negative DC voltage V_(dc) to the upper electrode 48 isprovided. In this configuration, the upper electrode 48 is provided atan upper portion of the chamber 10 via a ring-shaped insulator 102. Thering-shaped insulator 102 is made of, but not limited to, alumina(Al₂O₃). The ring-shaped insulator 102 hermetically seals a minute gapbetween a peripheral surface of the upper electrode 48 and a sidewall ofthe chamber 10, and physically supports the upper electrode 48 atnon-ground potential.

In the second example embodiment, the DC power supply unit 100 includestwo DC power supplies 104 and 105 having different output voltages(absolute values thereof); and a switch 108 configured to selectivelyconnect the DC power supplies 104 and 106 to the upper electrode 46. TheDC power supply 104 is configured to output a negative DC voltageV_(dc1) (e.g., about −2000 V to about −1000 V) having a relativelylarger absolute value, whereas the DC power supply 106 is configured tooutput a negative DC voltage V_(dc2) (e.g., about −300 V to about 0 V)having a relatively smaller absolute value. The switch 108 is operatedin response to a switching control signal SW_(ps) from the maincontroller 72. The switch 108 is configured to be switched between afirst switch position where the DC power supply 104 is connected to theupper electrode 46 and a second switch position where the DC powersupply 106 is connected to the upper electrode 46. Further, the switch108 also has a third switch position where the upper electrode 46 issuppressed from being connected to any of the DC power supplies 104 and106.

A filter circuit 112 is provided on a DC power feed line 110 to belocated between the switch 108 and the upper electrode 46. The filterunit 112 is configured to allow the DC voltage V_(dc1) (V_(dc2)) fromthe DC power supply unit 100 to be applied to the upper electrode 46therethrough and, also, allows a high frequency power introduced intothe DC power feed line 110 from the susceptor 16 through the processingspace PA and the upper electrode 46 to flow through a ground linewithout flowing into the DC power supply unit 100.

Furthermore, DC ground parts (not shown) made of a conductive materialsuch as Si or SiC are provided at appropriate positions facing theprocessing space PA within the chamber 10. The DC ground parts arecontinuously grounded via a ground line (not shown).

In the capacitively coupled plasma etching apparatus having theabove-described configuration, as for the kinds, forms, and combinationsof high frequency powers applied to the susceptor (lower electrode) 16within the chamber 10, the aforementioned first RF mode to the seven RFmode (see FIG. 2A to FIG. 3D) may be selectively used under the controlof the main controller 72 upon high frequency power feed units 33 and 35as the same as in the first example embodiment. Further, under thecontrol of the main controller 72 upon the high frequency power feedunits 33 and 35 and the DC power supply unit 100, it may be alsopossible to select an eighth RF mode or a (RF+DC) mode, as shown in FIG.18. By way of example, the eighth RF mode may be selected when modifyingan organic mask such as an ArF photoresist having low etching resistanceby injecting secondary ions generated in the upper electrode 46 into thesurface layer of the semiconductor wafer W at a high speed.

In the eighth RF mode, the high frequency powers RF1 and RF2 of the highfrequency power feed units 33 and 35 are set to have the same pulsewaveform with the same phase and the same duty ratio through the powermodulation. Further, by switching the switch 108, an output of the DCpower supply unit 100 is synchronized with the power modulation. The DCvoltage V_(dc1) having a large absolute value is applied to the upperelectrode 46 during an off-period T_(off), whereas the DC voltageV_(dc2) having a small absolute value is applied to the upper electrode46 during an on-period T_(on). A switching control signal SW_(ps) whichis in synchronization with the modulation control pulse signal PS issent to the switch 108 from the main controller 72. A ratio(V_(dc2)/(V_(dc1)+V_(dc2))) of time period during which the DC voltageV_(dc2) is applied within a single cycle of a pulse frequency depends onthe duty ratio of the high frequency powers RF1 and RF2.

Further, as one modification example of the eighth RF mode, the DC powersupply 106 may be omitted (or maintained off constantly), for example,and it may be possible to turn on and off an output of the DC powersupply 104 (i.e., to apply the DC voltage V_(dc1) only during theoff-period T_(off)) in synchronization with the power modulation, asdepicted in FIG. 19. Further, it may be also possible to use variable DCpower supplies as the DC power supplies 104 and 106.

In the eighth RF mode, two kinds of duty ratio control methods [8RFM-1,8RFM-2] may be selectively used. In the eighth RF mode, as depicted inFIG. 20A and FIG. 20B, when starting a process, the high frequency powerRF1 (high frequency power feed unit 33) for plasma generation is firstdriven at a time point t₀. Then, at a time point T₁ after a lapse of acertain time T_(a), the high frequency power RF2 (high frequency powerfeed unit 35) for ion attraction is driven. Thereafter, at a time pointt_(g) after a lapse of a certain time T_(b) (T_(b)>T_(a)), the DCvoltage V_(dc) (DC power supply unit 100) is driven.

Here, in the first duty ratio control method [8RFM-1], as shown in FIG.20A, at the time point T_(o) when starting the process, the duty ratioof the high frequency powers RF1 and RF2 and the DC voltage V_(dc) isset to be an initial value (e.g., about 90%) which allows plasma to beignited securely under any power modulating conditions (particularly, aduty ratio and a pulse frequency).

At the substantially same time of starting the process, the duty ratioof the RF1 and the RF2 and the V_(dc) is gradually reduced from theinitial value (about 90%) in a regular negative gradient or in a rampwaveform. At a time point t₂ after a lapse of a preset time T_(d)(T_(d)>T_(b)), the duty ratio has the originally set value D_(s) for theetching process. After the time point t₂, the duty ratio is fixed ormaintained at the set value D_(s) until the end (time point T₄) of theprocess. This first duty ratio control method [8RFM-1] may be effectivewhen plasma is difficult to be ignited in the eighth RF mode, e.g., whenthe duty ratio D_(s) is set to be low or a pulse frequency f_(s) is setto be high.

In the second duty ratio control method [8RFM-2], as shown in FIG. 20B,the duty ratio of the RF1 and the RF2 and the V_(dc) has the originallyset value D_(s) from the beginning (t₀) of the process to the end (t₃,t₄) of the process. This duty ratio control method [8RFM-2] may beappropriately used when it is possible to ignite plasma securely underthe duty ratio D_(s) and the pulse frequency f_(s) of the powermodulation performed in the etching process.

Further, in the plasma etching apparatus (FIG. 17) of the second exampleembodiment, it may be also possible to turn off the DC power supply unit100 and electrically separate it from the upper electrode 46. In such acase, it may be possible to use the aforementioned first RF mode to theseventh RF mode selectively, as in the plasma etching apparatus (FIG.1), and the above-described duty ratio control method may be used in thefourth RF mode to the seventh RF mode.

Other Example Embodiments or Modification Examples

From the foregoing, it will be appreciated that various embodiments ofthe present disclosure have been described herein for purposes ofillustration, and that various modifications may be made withoutdeparting from the scope and spirit of the present disclosure

By way of example, as shown in FIG. 21A, it may be possible to perform acontrol of reducing a duty ratio of the power modulation from an initialvalue (e.g., about 90% in the shown example) to a set value D_(s) instep shape during a transition time T_(d) immediately after a process isstarted. Alternatively, as depicted in FIG. 21B, it may be also possibleto perform a control of reducing a duty ratio to the set value D_(s)gradually (or in step shape) after a lapse of a certain elapse timeT_(k) immediately after the process is started. Here, in the aspect ofperforming a plasma process as desired under desired processingconditions, it may be desirable to shorten the elapse time T_(k). Mostdesirably, the elapse time T_(k) may be set to be zero (T_(k)=0) as inthe above-described example embodiments.

The high frequency power RF1 of the high frequency power feed unit 33suitable for plasma generation is described to be applied to thesusceptor (lower electrode) 16 in the above-described exampleembodiments. However, it may be also possible to apply the highfrequency power RF1 to the upper electrode 46.

The example embodiments may not be limited to the capacitively coupledplasma etching apparatus but may also be applicable to a certaincapacitively coupled plasma processing apparatus configured to performvarious plasma processes such as plasma CVD, plasma ALD, plasmaoxidation, plasma nitrification, sputtering, and the like. Further, theprocessing target substrate may not be limited to the semiconductorwafer, but various types of substrates for a flat panel display, anorganic EL or a solar cell, or a photo mask, a CD substrate, a printedcircuit board may also be used.

EXPLANATION OF CODES

-   -   10: Chamber    -   16: Susceptor (lower electrode)    -   33, 35: High frequency power feed unit    -   36, 38: High frequency power supply    -   40, 42: Matching device    -   43, 45: High frequency transmission line    -   46: Upper electrode (shower head)    -   56: Processing gas supply source    -   72: Main controller    -   94A, 94B: Matching controller    -   96A, 96B: Impedance sensor

1. A plasma processing method of generating plasma by a high frequencydischarge of a processing gas between a first electrode and a secondelectrode which are provided to face each other within an evacuableprocessing vessel that accommodates therein a substrate to be processed,which is loaded into or unloaded from the processing vessel, and ofperforming a plasma process on the substrate held on the first electrodeunder the plasma, the plasma processing method comprising: performing apower modulation on a first high frequency power for plasma generationin a pulse shape such that a first period during which the first highfrequency power is turned on or set to be a first level and a secondperiod during which the first high frequency power is turned off or setto be a second level lower than the first level are alternately repeatedat a regular pulse frequency in the plasma process; and setting a dutyratio in the power modulation of the first high frequency power to be aninitial value for plasma ignition, and then, reducing the duty ratiofrom the initial value to a set value for the plasma process graduallyor in a step shape during a preset transition time.
 2. The plasmaprocessing method of claim 1, wherein the reducing of the duty ratio inthe power modulation of the first high frequency power is started at thesubstantially same time of applying the first high frequency power toeither one of the first electrode and the second electrode.
 3. Theplasma processing method of claim 1, wherein the initial value of theduty ratio is set to be about 85% to about 95%.
 4. The plasma processingmethod of claim 1, wherein the transition time is set to be about 0.5second to about 3.0 seconds.
 5. The plasma processing method of claim 1,further comprising: applying a second high frequency power for ionattraction into the substrate from the plasma to the first electrodecontinuously at a preset constant power without performing the powermodulation thereon.
 6. The plasma processing method of claim 5, whereinthe applying of a second high frequency power to the first electrode isstarted after starting the reducing of the duty ratio in the powermodulation of the first high frequency power.
 7. The plasma processingmethod of claim 1, further comprising: applying a negative DC voltage tothe second electrode only during the second period in synchronizationwith the power modulation of the first high frequency power.
 8. Theplasma processing method of claim 1, further comprising: applying anegative DC voltage to the second electrode, wherein an absolute valueof the DC voltage during the second period is set to be larger than anabsolute value of the DC voltage during the first period insynchronization with the power modulation of the first high frequencypower.
 9. The plasma processing method of claim 7, wherein the applyingof the DC voltage to the second electrode is started after starting thereducing of the duty ratio in the power modulation of the first highfrequency power.
 10. The plasma processing method of claim 7, furthercomprising: applying a second high frequency power for ion attractioninto the substrate from the plasma to the second electrode only duringthe first period in synchronization with the power modulation of thefirst high frequency power.
 11. The plasma processing method of claim10, wherein the applying of the second high frequency power to thesecond electrode is started after starting the reducing of the dutyratio in the power modulation of the first high frequency power.
 12. Aplasma processing apparatus, comprising: an evacuable processing vessel;a first electrode configured to support a substrate to be processedwithin the processing vessel; a second electrode provided to face thefirst electrode within the processing vessel; a processing gas supplyunit configured to supply a processing gas into the processing vessel; afirst high frequency power feed unit configured to apply a first highfrequency power to either one of the first electrode and the secondelectrode to generate plasma of the processing gas within the processingvessel; a modulation controller configured to control the first highfrequency power feed unit to perform a power modulation on the firsthigh frequency power in a plasma process such that a first period duringwhich the first high frequency power for plasma generation is turned onor set to be a first level and a second period during which the firsthigh frequency power is turned off or set to be a second level lowerthan the first level are alternately repeated at a regular pulsefrequency; and a duty ratio controller configured to set a duty ratio inthe power modulation of the first high frequency power to be an initialvalue for plasma ignition, and then, reduce the duty ratio from theinitial value to a preset value for the plasma process gradually or in astep shape during a preset transition time.
 13. The plasma processingapparatus of claim 12, wherein the first high frequency power feed unitcomprises: a first high frequency power supply configured to output thefirst high frequency power under the control of the modulationcontroller and the duty ratio controller; a first high frequencytransmission line through which the first high frequency power outputtedfrom the first high frequency power supply is transmitted to either oneof the first electrode and the second electrode; a first matchingdevice, having a first impedance sensor and a first matching circuithaving a first variable reactance element provided on the first highfrequency transmission line, configured to measure load impedance by thefirst impedance sensor during a first monitoring time set within thefirst period in each cycle of the pulse frequency and control areactance of the first variable reactance element continuously such thata measurement value of the load impedance is equal to or approximate toa reference value corresponding to impedance on the side of the firsthigh frequency power supply; and a first monitoring time controllerconfigured to control the first monitoring time in proportion to theduty ratio in the power modulation of the first high frequency power.14. The plasma processing apparatus of claim 12, further comprising: asecond high frequency power feed unit configured to continuously outputand apply a second high frequency power for ion attraction into thesubstrate from the plasma to the first electrode at a preset constantpower.
 15. The plasma processing apparatus of claim 12, furthercomprising: a DC power supply unit configured to apply a negative DCvoltage to the second electrode only during the second period insynchronization with the power modulation of the first high frequencypower.
 16. The plasma processing apparatus of claim 12, furthercomprising: a DC power supply unit configured to apply a negative DCvoltage to the second electrode, wherein an absolute value of the DCvoltage during the second period is set to be larger than an absolutevalue of the DC voltage during the first period in synchronization withthe pulse modulation of the first high frequency power.
 17. The plasmaprocessing apparatus of claim 15, further comprising: a second highfrequency power feed unit configured to apply a second high frequencypower for ion attraction into the substrate from the plasma to thesecond electrode only during the first period in synchronization withthe power modulation of the first high frequency power.
 18. The plasmaprocessing apparatus of claim 17, wherein the second high frequencypower feed unit comprises: a second high frequency power supplyconfigured to output the second high frequency power under the controlof the modulation controller and the duty ratio controller; a secondhigh frequency transmission line through which the second high frequencypower outputted from the second high frequency power supply istransmitted to the first electrode; a second matching device, having asecond impedance sensor and a second matching circuit having a secondvariable reactance element provided on the second high frequencytransmission line, configured to measure load impedance by the secondimpedance sensor during a second monitoring time set within the firstperiod in each cycle of the pulse frequency and control a reactance ofthe second variable reactance element continuously such that ameasurement value of the load impedance is equal to or approximate to areference value corresponding to impedance on the side of the secondhigh frequency power supply; and a second monitoring time controllerconfigured to control the second monitoring time in proportion to theduty ratio in the power modulation of the first high frequency power.